/**
 * Copyright 2017 Pivotal Software, Inc.
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * <p>
 * https://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.micrometer.spring.export.prometheus;

import java.net.UnknownHostException;
import java.time.Duration;
import java.util.Map;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;

import org.springframework.scheduling.TaskScheduler;
import org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

import io.prometheus.client.CollectorRegistry;
import io.prometheus.client.exporter.PushGateway;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Class that can be used to manage the pushing of metrics to a {@link PushGateway
 * Prometheus PushGateway}. Handles the scheduling of push operations, error handling and
 * shutdown operations.
 *
 * @author David J. M. Karlsen
 * @author Phillip Webb
 * @since 1.1.0
 */
public class PrometheusPushGatewayManager {

    private static final Log logger = LogFactory
            .getLog(PrometheusPushGatewayManager.class);

    private final PushGateway pushGateway;

    private final CollectorRegistry registry;

    private final String job;

    private final Map<String, String> groupingKey;

    private final ShutdownOperation shutdownOperation;

    private final TaskScheduler scheduler;

    private ScheduledFuture<?> scheduled;

    /**
     * Create a new {@link PrometheusPushGatewayManager} instance using a single threaded
     * {@link TaskScheduler}.
     * @param pushGateway the source push gateway
     * @param registry the collector registry to push
     * @param pushRate the rate at which push operations occur
     * @param job the job ID for the operation
     * @param groupingKey an optional set of grouping keys for the operation
     * @param shutdownOperation the shutdown operation that should be performed when
     * context is closed.
     */
    public PrometheusPushGatewayManager(PushGateway pushGateway,
            CollectorRegistry registry, Duration pushRate, String job,
            Map<String, String> groupingKey, ShutdownOperation shutdownOperation) {
        this(pushGateway, registry, new PushGatewayTaskScheduler(), pushRate, job,
                groupingKey, shutdownOperation);
    }

    /**
     * Create a new {@link PrometheusPushGatewayManager} instance.
     * @param pushGateway the source push gateway
     * @param registry the collector registry to push
     * @param scheduler the scheduler used for operations
     * @param pushRate the rate at which push operations occur
     * @param job the job ID for the operation
     * @param groupingKey an optional set of grouping keys for the operation
     * @param shutdownOperation the shutdown operation that should be performed when
     * context is closed.
     */
    public PrometheusPushGatewayManager(PushGateway pushGateway,
            CollectorRegistry registry, TaskScheduler scheduler, Duration pushRate,
            String job, Map<String, String> groupingKey,
            ShutdownOperation shutdownOperation) {
        Assert.notNull(pushGateway, "PushGateway must not be null");
        Assert.notNull(registry, "Registry must not be null");
        Assert.notNull(scheduler, "Scheduler must not be null");
        Assert.notNull(pushRate, "PushRate must not be null");
        Assert.hasLength(job, "Job must not be empty");
        this.pushGateway = pushGateway;
        this.registry = registry;
        this.job = job;
        this.groupingKey = groupingKey;
        this.shutdownOperation = (shutdownOperation != null) ? shutdownOperation
                : ShutdownOperation.NONE;
        this.scheduler = scheduler;
        this.scheduled = this.scheduler.scheduleAtFixedRate(this::push, pushRate.toMillis());
    }

    private void push() {
        try {
            this.pushGateway.pushAdd(this.registry, this.job, this.groupingKey);
        }
        catch (UnknownHostException ex) {
            String host = ex.getMessage();
            String message = "Unable to locate prometheus push gateway host"
                    + (StringUtils.hasLength(host) ? " '" + host + "'" : "")
                    + ". No longer attempting metrics publication to this host";
            logger.error(message, ex);
            shutdown(ShutdownOperation.NONE);
        }
        catch (Throwable ex) {
            logger.error("Unable to push metrics to Prometheus Pushgateway", ex);
        }
    }

    private void delete() {
        try {
            this.pushGateway.delete(this.job, this.groupingKey);
        }
        catch (Throwable ex) {
            logger.error("Unable to delete metrics from Prometheus Pushgateway", ex);
        }
    }

    /**
     * Shutdown the manager, running any {@link ShutdownOperation}.
     */
    public void shutdown() {
        shutdown(this.shutdownOperation);
    }

    private void shutdown(ShutdownOperation shutdownOperation) {
        if (this.scheduler instanceof PushGatewayTaskScheduler) {
            ((PushGatewayTaskScheduler) this.scheduler).shutdown();
        }
        this.scheduled.cancel(false);
        switch (shutdownOperation) {
            case PUSH:
                push();
                break;
            case DELETE:
                delete();
                break;
        }
    }

    /**
     * The operation that should be performed on shutdown.
     */
    public enum ShutdownOperation {

        /**
         * Don't perform any shutdown operation.
         */
        NONE,

        /**
         * Perform a 'push' before shutdown.
         */
        PUSH,

        /**
         * Perform a 'delete' before shutdown.
         */
        DELETE

    }

    /**
     * {@link TaskScheduler} used when the user doesn't specify one.
     */
    static class PushGatewayTaskScheduler extends ThreadPoolTaskScheduler {

        PushGatewayTaskScheduler() {
            setPoolSize(1);
            setDaemon(true);
            setThreadGroupName("prometheus-push-gateway");
        }

        @Override
        public ScheduledExecutorService getScheduledExecutor()
                throws IllegalStateException {
            return Executors.newSingleThreadScheduledExecutor(this::newThread);
        }

    }

}
